1. Field of the Invention
The present invention relates to a process of production of a compressor shoe.
2. Description of the Related Art
The refrigeration circuit used in a car air-conditioner includes a compressor for compressing refrigerant gas. For example, in a known variable displacement swash plate type compressor, as shown in FIG. 7, a cylinder block 91 is formed with a plurality of cylinder bores 91a. Pistons 92 are accommodated in these cylinder bores 91a to be able to reciprocate in them. Further, a swash plate 93 able to synchronously rotate and be inclined is supported by a not shown rotatably supported drive shaft. Between the swash plate 93 and each piston 92 is provided a pair of shoes 94 sandwiching the swash plate 93. Each shoe 94, as illustrated in FIG. 8, has a top surface forming part of a spherical surface as a spherical part 94a and bottom surface forming a substantially flat surface as the flat part 94b. A cylindrical part 94c is formed through rounded portion.
In a compressor configured in the above way, due to the rotation of the drive shaft, as shown in FIG. 7, the swash plate 93 synchronously rotates and inclines to cause the pistons 92 via the shoe 94 to reciprocate inside the cylinder bores 91a. Due to this, refrigerant gas is sucked in, compressed, and discharged at the head sides of the pistons 92. The spherical parts 94a of the shoes 94 slide with the surfaces of the spherical seats 92a of the pistons 92, while the flat parts 94b slide with the surface of the swash plate 93. Therefore, the shoes 94 are subjected to a large frictional force between the pistons 92 and the swash plate 93, so the shoes 94 are required to have abrasion resistance and a long fatigue life.
In the past, such a shoe 94 was manufactured by the following method (shown in FIG. 1). That is, first, a blank ball 80 was fabricated from the high carbon chrome bearing steel SUJ2 (JIS G4805).
Here, SUJ2 is comprised of the following:                Carbon: 0.95 to 1.10 wt %        Chrome: 1.30 to 1.60 wt %        Manganese: 0.5 wt % or less        Silicon: 0.15 to 0.35 wt %        Phosphorus: 0.025 wt % or less        Sulfur: 0.025 wt % or less        
Further, the blank ball 80 is obtained by cutting out an amount of material enabling formation of a shoe from a rod member comprised of the above SUJ2, forming this material into a spherical shape, then quenching, tempering, polishing, and annealing it.
Next, as shown in FIG. 1, the blank ball 80 is formed into a material 81 of a shoe shape by a press process S71. Next, the material 81 is subjected to a quenching process S72 in a quenching furnace to obtain a quenched shoe 82 given a high hardness. Further, the quenched shoe 82 is subjected to a tempering process S73 in a tempering furnace to obtain a heat treated shoe 83 maintaining its high hardness and given toughness. Finally, a polishing process S74 is applied to the heat treated shoe 83 to obtain the compressor shoe 94.
The thus manufactured shoe 94 is given a high hardness by the application of the quenching process S72 to the material 81 and is given a high toughness by the application of the subsequent tempering process S73, so the required abrasion resistance and long fatigue life are realized.
In a shoe manufactured by the above process of production of the related art, if the heat treated shoe 83 is not sufficiently polished, the durability becomes insufficient, so a long time is required for the polishing process S74 and the costs of manufacture end up skyrocketing.